Launched munitions projectiles are generally referred to as "combat rounds." For the purposes of this application they are referred to herein as "projectiles." Designing combat round fuzing systems for munitions systems has become a rather sophisticated design challenge. This is due to several factors that must be considered in contemporary designs, including safety factors, increasing functional density requirements, and restrictions on volume. These and other factors have combined to complicate the design of combat round fuzing.
One of the many functions required of a combat round munitions fuze is the ability to reliably detonate the projectile on impact. As will be appreciated by those skilled in the art, a combat round that does not detonate upon impact remains a hazard to human life and property until it is removed, detonated or disarmed. It will also be appreciated that the proper disposition of undetonated combat rounds is extremely expensive and dangerous. Unfortunately, many of the fuzes currently employed in the art do not reliably detonate the combat round upon impact at slight grazing angles, thus, often creating such hazardous conditions.
In addressing the detonation requirements for detonating a combat round, there are at least two types of impact detonation that must be considered in the design of a combat round fuze. The first type of impact is a "head-on" impact which occurs when the projectile hits a target head-on. A "head-on" impact results in the projectile being subjected to a high deceleration force directed mainly along its longitudinal axis. Designing for a "head-on" impact customarily employs some type of "crush switch" mechanism. As known in the art, a crush switch provides electrical switch closure of a pair of contacts as the nose of the projectile collapses upon impact of the projectile upon the target. The closed pair of contacts, in turn, activate detonation control electronics that initiate the fuze detonation process.
The second type of impact considered is a "non-head-on" impact which occurs when the round does not hit head-on, but rather, grazes a target. For a "non-head-on" impact, a crush switch may not reliably provide the switch contact closure function needed to detonate the fuze. This is particularly a problem if the target impact graze angle is too slight to activate the crush switch. At such a slight target impact angle, a diminished or incomplete crushing of the combat round nose may result in a lack of detonation.
One example of a crush switch often used in combat round munitions applications is an impact switch commonly known as a Lucey Switch, in honor of its inventor. One such impact switch is specified in Army Research Lab Specification Control Drawing for Part. No. #11718418, entitled "IMPACT SWITCH." In the specified impact switch, a spring is employed for exerting a selected spring force substantially against a conically shaped electrical contact. Upon impact of the projectile against a target, the spring collapses, thereby allowing the conically shaped electrical contact to electrically connect with a receiving electrical contact to initiate activation of a fuze resulting in detonation of the projectile.
Other factors must also be considered in fuze designs, for example, in many combat round munitions applications, as well as other munitions applications, firing of the projectile must be detected before detonation of the fuze. Firing of the projectile is referred to as the "firing event." In essence, detection of the firing event enables firing event detection electronics to initiate time dependent functions. An apparatus including firing event detection electronics is sometimes referred to as a setback detector.
A firing event setback detector is generally constructed so as to only detect the occurrence of an acceleration along the firing axis. Generally, the firing axis coincides with the longitudinal axis of the projectile since the velocity component along the firing axis increases rapidly from zero velocity before the firing event to a very high velocity after the firing event. In an ideal setback detection mechanism, the setback detector would provide a setback detection signal when the setback force along the firing axis increases above a selected acceleration threshold so as to provide a safety margin against premature detonation of the combat round. At the other extreme, an ideal impact detection mechanism would provide an impact detection signal under any deceleration condition along the firing axis above a selected deceleration threshold, so as to also provide a safety margin to assure detonation upon impact.